Amy Jenkins: Martin Amis's failing is mine too

So Anna Ford thinks Martin Amis is a narcissist. She may be right – but the fact that he's a useless godparent is not good evidence. Ford has complained that Amis "paid scant attention" to her daughter Claire and "didn't even cough up the statutory five bob expected".

Surely, you're allowed to resist jumping through sentimental hoops without being a narcissist? Because for every wonderful fairy godmother out there, there's a bad fairy creeping around limp-winged with guilt. Someone like me. Someone who's not good at remembering birthdays, who still hasn't bought the silver christening spoon, who can't afford to lay down the case of fine wine that will mature at the same rate as a dear friend's beloved offspring.

The thing is, being a godparent is an extremely tricky business. For a start, unless you're a natural Mary Poppins, it's hard to make friends with other people's children. (Frankly, it's sometimes a challenge to find them interesting.) Young children don't relate to adults who aren't family unless those adults put a large amount of work in. To figure in a child's universe you need to visit often bearing large and exciting presents. And not any old presents. The right presents. This requires extensive research, otherwise the child will crow: "Got it already!" and sling your gift to one side with some glee.

Of course, they'll eventually grow out of being rude – but then you've got a sulky teenager to contend with. Perhaps you'll take them on an expensive night out to a hit London musical. Perhaps they'll fidget beside you all evening, sending furtive texts on their i-phone. Perhaps when it's over they'll say: "That was-" "Yes?" you say expectantly... gratitude at last? "Long! That was so long."

With a teenager, you're better off thrusting money into their hand, but even that can be hard to pull off. A godchild is not a bell boy. The age of tipping children as a matter of course is long gone. Sadly, that five bob Anna Ford talks about isn't statutory. If it were, things might be different.

Being a godparent is so tricky because the rules are ill-defined. What exactly are you meant to provide and when? What are the parents expecting of you? Some parents appoint you and then get scared that you're going to muscle in. One friend teased me that, as godmother, I was meant to provide moral guidance to his son. As he talked his wife kept interjecting: "No she doesn't!", somewhat alarmed.

Clearly, godparenting can queer the pitch of friendship. Roles are unclear and there's a kind of forced intimacy. Friendship doesn't respond well to forcing. I haven't lost many friends over the years. Some friendships have drifted off, run their course or simply been outgrown. That's natural – but the two friends I've most painfully fallen out with are both men who asked me to godparent a child. In fact, I have two little god-orphans.

All that being said, when godparenting does work out it can be glorious. I have a lovely godmother but – guess what – I chose her myself. It's the only way to do it. She was an old friend of my mother's who I re-met in my early twenties. As our friendship grew – unforced – she began to refer to herself as my godmother and now the idea is so much part of our bond that both of us believe it.